Dynamic Stark Effect in Two-Dimensional Spectroscopy Revealing Modulation of Ultrafast Charge Separation in Bacterial...

Area of Science:

• Biophysics
• Photosynthesis research
• Quantum biology

Background:

• Photosynthetic reaction centers (RCs) exhibit highly efficient ultrafast charge separation.
• The precise mechanisms governing this efficiency remain incompletely understood.
• Intradimer charge-transfer intermediates play a crucial role in this process.

Purpose of the Study:

• To investigate the role of inherent electric fields in ultrafast charge separation within photosynthetic RCs.
• To correlate the formation of the P_A⁺P_B^- intermediate with charge separation rates.
• To elucidate the influence of electric field modulation on electron transfer dynamics.

Main Methods:

• Recording ultrafast two-dimensional electronic spectra of purple bacterial RCs at 77 K.
• Utilizing transient Stark spectroscopy to detect inherent electric fields.
• Comparing wild-type and three mutated RCs to analyze mutation-specific effects.

Main Results:

• Transient Stark signals, indicative of an inherent electric field, were observed in the spectra.
• A correlation was established between efficient P_A⁺P_B^- formation and faster charge separation rates.
• Mutations altered the electric field's orientation and amplitude, leading to varied electron transfer rates.

Conclusions:

• The inherent electric field of the P_A⁺P_B^- intermediate modulates electron transfer rates.
• This modulation mechanism reconciles experimental findings with activation energy theory.
• Provides a new perspective on controlling charge separation efficiency in RCs.